1. Field of the Invention
The present invention relates to a polymerization apparatus for polymerizing a monomer having an ethylenically unsaturated double bond by polymerizing the monomer while circulating the reaction mixture through a heat exchanger placed separately from a polymerization vessel and a method of producing a polymer by using said polymerization apparatus.
2. Description of the Prior Art
Polymerization of a monomer having an ethylenically unsaturated double bond is carried out in such a manner that a polymerization medium, such as water, a dispersant, a polymerization initiator, the monomer having an ethylenically unsaturated double bond, and, if necessary, other various additives are charged into a polymerization vessel equipped with a water jacket and a reflux condenser, then the temperature in the polymerization vessel is elevated, and the polymerization reaction is performed with the temperature kept constant. During that polymerization reaction, to keep the temperature in the polymerization vessel constant, since it is required to remove the heat of the polymerization reaction, cooling water is circulated through the water jacket and the reflux condenser.
In recent years, in order to improve the productivity, it is carried out to (1) make the size of a polymerization vessel large, and (2) shorten the polymerization time per batch. However as the size of polymerization vessels is made large, since the ratio of the heating surface area for the reaction mixture to a unit volume is decreased, the conventional method of removing the heat of polymerization reaction becomes unsatisfactory in the capacity of removing the heat. Further, if the polymerization time per batch is shortened, since the rate of heat generation due to the polymerization reaction per unit time is increased, the capacity of removing heat becomes unsatisfactory.
Several methods of overcoming these disadvantages are suggested and, among them, as an effective method can be mentioned one in which the reaction mixture is circulated through a heat exchanger placed outside a polymerization vessel (see Japanese Pre-examination Patent Publication (KOKAI) Nos. 54-24991, 56-47410, and 58-32606 and Japanese Patent Publication (KOKOKU) No. 64-11642). This method is quite efficient in that the ratio of the heating surface area for the reaction mixture to a unit volume can be increased.
However, according to this method, there are problems of the operation and the quality that due to polymers in the form of scale or blocks produced in the circuit consisting of the heat exchanger and the circulation pipeline connecting that heat exchanger to the polymerization vessel, tubes of the heat exchanger are clogged or fish eyes are increased when the obtained polymer is formed into a sheet or the like.